The invention relates to a pallet truck or pallet jack in which a fork-like member projecting from a main frame is used for raising and lowering a load positioned upon a pallet for subsequent relocation of the load. A hydraulic system is used for raising and lowering the fork member, under which are provided a plurality of rollers by which the pallet truck is moved. Typically, a linkage system links the tines of the fork member to the hydraulic system for the carrying out of the lowering and raising of the fork member.
It has been known to provide weighing load cells on the tines of the fork member in forklifts, and the like. Such prior art load cells, however, are not readily usable by the fork member of a pallet truck because the vertical lifting displacement of the fork member is within a very narrow range, compared with a forklift truck. In a conventional forklift, the fork member is raised and lowered over a considerable vertical distance, for not only lifting and moving a load, but also for stacking the load; whereas in a pallet truck, the fork member is lifted a very limited vertical distance in order to move the load from one location to another, without the possibility of stacking the loads. Thus, because the vertical distance moved by the fork member of a pallet truck is quite limited, prior art weighing load cells and devices used in conventional forklift trucks would not readily be adaptable to a pallet truck owing to the lack of space beneath the fork member, since mounted underneath thereof are the wheels or rollers. This is not the case in conventional forklifts where there are no wheels or wheel bases provided under the fork member.
U.S. Pat. No. 3,431,992 discloses a pallet lift having a hydraulic load cell on each tine thereof, for weighing a load emplaced upon the fork member of the device. However, the load cells are constituted by a reciprocating piston attached to a load-bearing rod for lifting the load, for the eventual weighing thereof by a hydraulic pressure system. The system of this patent is quite complicated, and inaccurate and can only indicate weight and not any other weighing function, and necessitates separate steps for weighing the load. Further, the initial lifting of the device is undertaken by the piston rods of the weighing system alone, without any support by the tines of the fork member. In addition, after weighing the load, these piston rods are retracted to allow the weight to be carried by the fork member, but in so doing, owing to the differences in timing by the retraction of the piston rods, the load and the pallet on the fork member may be misaligned and/or improperly oriented, especially in cases where the load being carried is lighter than normal. Further, this system could result in pallet-breakage in the cases where the load is not on the pallet cross-bars.